It has been proposed to feed liquid to an applicator with an apparatus consisting of an inner liquid container in which the liquid may be supplied to the user and an outer pressure vessel. Although the provision of an inner and outer container may at first sight seem unnecessary, such a two container system has been found to possess various advantages: for example, it makes the system cleaner to use and it makes cleaning of the system after use easier.
In our International patent application, publication No. WO 80/00315, an apparatus for applying liquid to a surface is described. In one of the embodiments described the apparatus has an inner paint container and an outer pressure vessel. In use pressurized gas is injected into the interior of the outer vessel and passes into the inner paint container and expels paint from the inner container through a dip tube to an applicator connected to the apparatus by a flexible tube. It is proposed that paint is supplied to the user in the inner paint container which the user inserts into the outer vessel before use. Since it is proposed that the paint be supplied to the user in the inner paint container, it is important that this container be of relatively simple and cheap construction.
In U.S. Pat. No. 3,640,630 a paint applicator is described in which a portable pressurized container is provided into which a paint container in the form of a flexible plastics bag may be inserted. In order to regulate the pressure in the container, the container forms a seal with a wall of an outer vessel and when the pressure exceeds a threshold value, the seal is broken until the pressure returns to below the threshold value.
We have found that, in order to ensure satisfactory feeding of the paint to the applicator and satisfactory application by the applicator, the paint should possess special physical properties. It is therefore desirable that the apparatus be able to be used only with paint which has been designed specifically for use with the apparatus. The use of an unsuitable liquid may also damage the apparatus.
With the apparatus of U.S. Pat. No. 3,640,630, it would be possible for a user to take a conventional can of paint, remove the lid and place the can in the outer container, or alternatively pour paint into the outer container. The apparatus could then be operated in the usual manner using the conventional paint.
Similarly, in the embodiment of our International patent application described above, it would be possible for a user to place a conventional paint can, instead of the inner paint container containing special paint, inside the outer vessel, or alternatively pour paint into the outer vessel. The apparatus therefore also has the disadvantage that it can be used with unsuitable paint. Although there is a reference in International patent application No. WO 80/00315 to providing means for preventing the insertion of an unsuitable container this would not prevent paint being poured directly into the outer vessel.
Various pressurizing assemblies for use in feeding liquid to an applicator are known. Our international patent application, publication No. WO 80/00315, published Mar. 6, 1980, describes and shows in FIG. 3 thereof a particular form of such pressurizing assembly, our British patent application, publication No. 2,066,932, published July 5, 1981, describes other suitable forms of pressurizing assembly, and both these descriptions are hereby incorporated herein by reference.